Jason Here is a diagram of a Ford coil internal wiring. The wiring on other coils is always electrically the same, but can be physically different. An open secondary winding is by far the most common fault. If the winding is defective the coil is usually no economically repairable. Remember they made 75,000,000 Model T coils and finding another is easy. Other internal wiring faults can easily be repaired. You also need to carefully inspect the coil box terminals. They are two piece construction and can be open between the parts because of corrosion. Flowing a bit of solder over the terminal will usually correct this problem. Ron the Coilman

Jim Your correct and you will find that latent fault in one out of every 75-100 coils during rebuilding. You detect this fault during the rebuilding process, when the old capacitor is removed and before the new capacitor has been installed, using a 1000volt a Megger connected across the two windings. Ron the Coilman

The Montana 500 guys from Spokane get angry with me because they think I talk too much. They like to keep some of their secrets under their hat as they are worried about Garrett Green and the Californian bunch. Even though I'm sure Garrett has thought of everything we've done already. As such, I will be a little cagey.

Have you read the Montana 500 newsletter articles that I referenced in some of these threads, namely the "Bucket Analogy" and the "Coil Comparison" articles? If you have any specific questions about something that I wrote that was not clear, feel free to ask them.

Don't get too hung up about impedance and Q-factor. It isn't that big of deal when driving at "normal" speeds, say up to 45 MPH. But, if you are interested in high speed, there is a reason we Montana 500 drivers want a high Q-factor. This is a clue to one thing we do with our coils. Cryptic, I know, but ask yourself why we would want coils with a high Q-factor. If you can figure this out you are on your way to a major speed secret. I will say no more on this at this time.

We all run Anderson style timers which we make sure are well timed. For that I have a huge degree wheel that I attach to the radiator and use the starting crank as an indicator.

Jim Thode A good quality Chinese 1000 volt Megger costs $60 on Ebay. In my view, if you rebuild any more than a few coils it is a great trouble shooting tool that will save you time. Remember my favorite saying; "if you need a tool and don't buy it, soon you will find out you paid for it and don't have it". But, I am always mindful of the favorite saying of my Colorado Model T Friend; "some Model T folks wouldn't spend five dollars to get cured of cancer" Grin Have fun. Ron the Coilman